A board printing apparatus performing mask-printing on a board is known in general. Such a board printing apparatus is disclosed in Japanese Patent Laying-Open No. 2006-066811, for example.
Due to miniaturization of electronic components mounted on a printed board, 0603 size (0.6 mm×0.3 mm) or 0402 size (0.4 mm×0.2 mm) small components (very small components) and large components such as a shield component are mixed and mounted on the board. When a viscous material such as solder is printed on the board to mount these components, an appropriate amount of transfer of the viscous material to be printed is generally determined according to the size of a component according to the size of the component.
Japanese Patent Laying-Open No. 2006-066811 discloses a technology to print solder using a single mask (so-called half etching mask) having a large thickness in a printing area corresponding to a large component and a small thickness in a printing area corresponding to a small component (very small component). The amount of transfer of a viscous material on a board corresponds to the thickness of the mask, so that the viscous material can be printed with the amount of material according to the size of a component by using the half etching mask. When the mask disclosed in Japanese Patent Laying-Open No. 2006-066811 is used, however, a step (a boundary between the thickness for the large component and the thickness for the small component) is formed in the printing area, and stable printing pressure for filling an opening with the viscous material cannot be ensured in the vicinity of this step. Thus, a circuit pattern (an opening pattern of the mask) must be formed to avoid the vicinity of the step. Therefore, according to the printing technology disclosed in Japanese Patent Laying-Open No. 2006-066811, the integration degree of a circuit cannot be improved.
Two types of masks, a first mask for the small component having the small thickness and a second mask for the large component having the large thickness, are conceivably prepared to sequentially perform printing. A relief portion is provided on the board contact surface of the second mask to relieve a pattern of a transfer material formed by the first mask, whereby a printing pattern for the large component can be formed by the second mask after a printing pattern for the small component (very small component) is formed by the first mask.
When the two types of masks are used, however, two board printing apparatuses must be provided to create a production line for sequentially performing printing, and hence the structure of the production line is disadvantageously complicated.